Release 2.5.7.1

Maintenance release:

• Add sourcemap files: browser-polyfill, purify (issue #149, #104)
• Disable debug logs and fix error getting host when showing contextmenu (issue #157)
• Fix errors being logged when sent messages have no receiver
• Fix column visibility list not showing active columns
• Fix error adding MutationObserver to framesets (#153)
• Update Russian, Korean and Greek translations (#113, #132, #135, #158, #159)